Deleting an already deleted image using admin user is throwing an
error "404 Not Found" which is confusing. Deleting an image that does
not exist throws "No image with a name or ID of 'image-id' exists."
Updated the code so that trying to delete an already deleted image
throws "No image with an ID of 'image-id' exists." error.
Closes-Bug: #1333119
Change-Id: I8f9a6174663337a0f48aafa029a4339c32eb2134
Co-Authored-By: Abhishek Talwar <abhishek.talwar@tcs.com>
Co-Authored-By: Kamil Rykowski <kamil.rykowski@intel.com>